Helicopter lineman&#39;s ladder and method for energized powerline repair

ABSTRACT

A rigid, unitary ladder is provided having one end which attaches to a powerline support tower after the ladder is dropped by helicopter to a lineman previously offloaded onto the tower. The ladder includes a first section which extends outwardly from the tower and a second section which extends angularly downward from the first section to a base which rests on the powerline. The first section is of a length sufficient to space the base a distance from the tower which is beyond the flashover area around the tower.

BACKGROUND OF THE INVENTION

High voltage powerlines carrying voltages in the hundreds of kilowattrange have been constructed to extend from spaced towers high aboveterrain which is often practically inaccessible to land vehicles. Inrecent years, a number of methods and devices have been developed tofacilitate the repair of remote high voltage powerlines which areaccessed by helicopter.

Helicopter transported landing platforms and work scaffolds which can beattached to the cross arm of a utility pole have been developed topermit a lineman to disembark from a helicopter and descend verticallyalong the utility pole to the powerlines supported thereby. Such devicesare heavy and bulky, and are often difficult to maneuver. Moreimportantly, however, is the fact that these devices position a linemanin close proximity to a grounded utility pole, so that the powerlinesmust be deenergized before repair can occur. Otherwise it is dangerousfor a lineman to remain in the electrically charged space betweenenergized high voltage conductors and a grounded tower or utility pole.A helicopter-mountable landing platform and work scaffold adapted to bemounted by a utility pole is illustrated in U.S. Pat. No. 3,863,736 toMcWilliams.

In order to avoid an extensive power outage which might occur when ahigh voltage powerline is deenergized for repair, it is desirable toprovide live maintenance on energized high voltage conductors. Toaccomplish this, linemen first bond to the energized transmission lineto become energized to the same potential as that of the line. Thispermits the lineman to work safely on the energized line so long as hemaintains sufficient spacing from grounded structures, such as supporttowers, to prevent the risk of flashover. To facilitate live maintenanceon energized high voltage powerlines, various lineman support structureshave been developed which are suspended from a helicopter over apowerline pair remote from the support towers. These support structuresare formed either partially or totally from electrically conductivematerial and include skids or rollers which engage a pair of parallellines. Such lineman support structures are shown by U.S. Pat. Nos.4,478,312 to Kurtgis and 5,494,132 to Hansen. Not only are thesestructures bulky and somewhat cumbersome, but it is difficult toposition the conductive skids or rollers on the energized powerline pairfrom a helicopter. Also, these support structures may inadvertently moveinto dangerous proximity with a grounded tower structure.

In an attempt to eliminate bulky, difficult to position, linemen supportplatforms, systems have been developed for lowering a lineman from ahelicopter directly onto an energized powerline. U.S. Pat. No. 4,673,059to Kurtgis discloses such a system. Not only is there some difficulty inaccurately positioning a lineman at the end of an elongate, swingingcable adjacent to an energized powerline for a time sufficient tocomplete a safe interconnection with the powerline, but once on thepowerline, the lineman, through inattention, may move too close to agrounded tower.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a novel andimproved helicopter lineman's ladder and method which permits a linemanto be directly landed from a helicopter onto a stable powerline supporttower.

Another object of the present invention is to provide a novel andimproved lineman's ladder which is lightweight and which can be loweredfrom a helicopter and easily positioned between a tower cross arm andenergized conductors by a single lineman.

Yet another object of the present invention is to provide a novel andimproved helicopter lineman's ladder which will deliver a lineman from atower to energized powerlines and insure that the lineman is a safedistance from the tower before the lineman bonds to an energizedpowerline.

A still further object of the present invention is to provide a noveland improved helicopter lineman's ladder which operates to prevent alineman who has bonded to an energized powerline from inadvertentlymoving dangerously close to a grounded tower.

These and other objects of the present invention are achieved byproviding a rigid ladder having one end which hooks to a powerlinesupport bridge after the ladder is dropped by helicopter. The ladderincludes a first section which extends out from the support bridge forthe flashover distance to the tower or more, and a second section thatextends downwardly from the outer end of the first section to a basewhich rests on the powerlines spaced from the support bridge. A weighton the base holds it against the powerlines, and the complete structureis formed of electrically nonconductive material. Using this structure,when a lineman hooks up to the powerline, he will be more than theflashover distance from the support bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of high voltage tower supported powerlines;

FIG. 2 is a perspective view of the helicopter lineman's ladder of thepresent invention;

FIG. 3 is a view in side elevation of the helicopter lineman's ladder ofFIG. 2; and

FIG. 4 is a perspective view of a second embodiment of the helicopterlineman's ladder of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, high voltage AC transmission lines normallyinclude at least three powerline conductors 2, 4 and 6, with eachpowerline conductor carrying a voltage which is 120° out of phase withthe voltages carried by the remaining conductors. These powerlineconductors extend over substantial distances and are supported to extendbetween spaced towers 8 and 10. Each powerline conductor is suspendedbeneath a tower cross arm 12 by elongate insulators 14.

In accordance with the method of the present invention, a helicopter 16offloads one or more linemen 18 directly onto a tower 8. This can beaccomplished by having linemen sit on a helicopter skid 20 or upon aplatform placed across the helicopter skids which extends laterally ofthe helicopter. By having the helicopter directly deposit linemen onto astable tower structure which is insulated from the powerline conductors,unstable tethers which can swing a lineman into an energized powerlineare eliminated.

Once the lineman is on the tower, the problem to be solved is how thelineman can safely descend to the energized powerline conductors 2, 4and 6 and bond onto a conductor to raise his body voltage to thepowerline conductor voltage. This cannot be done from the grounded towerstructure or even from within an area close to the tower structure whereflashover can occur. A flashover area, indicated at 22, must be avoidedif live maintenance on energized powerline conductors is to be safelyaccomplished. OSHA safety regulations require that a flashover area ofat least eleven feet from the tower be maintained for energized highvoltage transmission line repair and that this area must be avoided bylinemen bonded to a powerline conductor.

In accordance with the present invention, a one piece, unitary lineman'sladder indicated generally at 24 is provided to ensure that a linemancan safely descend from the tower, bond onto an energized conductor,accomplish conductor repair, and ascend back to the tower without dangerof ever entering the flashover area 22 while energized. The lineman'sladder 24 includes a first elongate section 26 having a free end whichterminates in a pair of spaced connectors 28 which are adapted to engageand be connected to the tower cross arm 12 of a tower 8. Theseconnectors are shown as hooks in FIG. 1, but may take a number of formsto permit a lineman to positively lock the free end of the elongatesection 26 to the tower cross arm. These connectors can be, for example,hooks with pivoted locking arms, hooks in combination with belts tosecure the ladder to the cross arm, belts alone, or other known lockingconnectors to secure the ladder to the cross arm.

A second elongate section 30 of the lineman's ladder extends from theend of the section 26 at an angle no less than ninety degrees and whichis preferably greater than ninety degrees. The section 30 terminates ina curved base bar 32 which extends outwardly on either side of thesection 30 and terminates in downwardly turned ends 34 and 36. Extendingbelow the base bar on a flexible tether 38 is a weight 40.

The elongate sections 26 and 30 of the lineman's ladder 24 are formed asladder sections with spaced side bars 42 joined by cross rungs 44. Allcomponents of the lineman's ladder, including the sections 24 and 30,the connectors 28, the base bar 32, the tether 38 and the weight 40 arepreferably formed of electrically nonconductive material. The ladder isvery light weight and maneuverable and can easily be carried and loweredfrom a helicopter and secured in place by a lineman who was previouslyoffloaded onto the tower 8.

An important feature of the lineman's ladder 24 is the length of theelongate section 26. The length of this section must be sufficient toinsure that a lineman descending down the section 30 to an energizedline is outside the flashover area 22. Ideally, the length of thesection 26 is eleven feet or more to position the section 30 outside theflashover zone. The section 30 will normally be shorter than the section24 as its length must merely be sufficient to enable a lineman to reachthe conductors supported below the tower cross arm 12.

In accordance with the present invention, once the lineman is offloadedfrom the helicopter onto the tower, the lineman's ladder 24 is loweredto the lineman from the helicopter. Rings 46 may be secured to thesidebars 42 between the sections 26 and 30 to facilitate attachment to ahelicopter cable. The lineman positions the ladder over a conductor orconductors and attaches the spaced connectors 28 to the tower cross arm12. Then the base bar 32 is lowered into engagement with a conductor orconductors and is held in place by the tethered weight 40. The linemannow descends to the base bar, and while standing on the insulated basebar, bonds to the energized conductor. Now, the lineman can step ontothe conductor to perform repairs. With the lineman's ladder in place,access to the flashover zone is blocked to prevent the lineman frominadvertently straying into the flashover zone while his attention isfocused on repairing an energized conductor. Once the repair has beencompleted, the lineman steps back on the base bar 32 and terminates thebond with the energized conductor. Now the lineman can ascend back ontothe tower 8, and assist in removal of the lineman's ladder by thehelicopter.

FIG. 4 illustrates a second embodiment of the unitary lineman's ladderwhich is indicated generally at 48. Here structural elements which arethe same as those previously described with reference to FIGS. 2 and 3will be designated with like reference numerals.

In the lineman's ladder 48, the ladder rungs 44 in elongate section 26are eliminated and a solid ramp 50 extends between the sidebars 42. Alsohandrails 52 are attached to the sidebars 42 of the elongate section 26on either side of the ramp 50. These handrails can be attached to ahelicopter lowering cable.

In the lineman's ladder 48, the base bar 32, tether 38 and weight 40 ofthe lineman's ladder 24 are replaced by a platform 54 secured to thebottom of the section 30. This platform supports weights 56 shown bybroken lines in FIG. 4 which hold the platform in engagement with anenergized conductor. Downward spaced projections 58 formed on eitherside of the bottom of the platform 54 extend on either side of aconductor which the platform engages. Preferably, all components of thelineman's ladder 48 are formed of electrically nonconductive material.

I claim:
 1. A helicopter lineman's ladder in combination with a towerhaving a cross arm supporting energized high voltage powerlineconductors to position a lineman on a powerline conductor at a positionoutside a flashover area which extends at a distance around said tower,said ladder comprising: a first elongate ladder section having a freeend to be attached to said cross arm of said tower, at least oneconnector mounted on the free end of said first elongate ladder sectionfor connecting said free end to said cross arm of said tower, a secondelongate ladder section extending angularly from an end of said firstelongate ladder section opposite to said free end thereof, and apowerline conductor engaging base secured to an end of said secondelongate ladder section and resting on the powerline conductor beyondsaid flashover distance, said first elongate ladder section being ofsufficient length to position said powerline conductor engaging base incontact with a powerline conductor at a point spaced from said towerwhich is a greater distance from said tower than said flashover distancewhen said connector connects the free end of said first ladder sectionto said cross arm of said tower.
 2. The helicopter lineman's ladder ofclaim 1 wherein at least one weight is secured to said conductorengaging base.
 3. The helicopter lineman's ladder of claim 1 whereinsaid first and second ladder sections are unitary.
 4. The helicopterlineman's ladder of claim 3 wherein said second ladder section extendsangularly from said first ladder section at an angle at least equal toninety degrees.
 5. The helicopter lineman's ladder of claim 4 whereinsaid second ladder section extends angularly from said first laddersection at an angle greater than 90 degrees.
 6. The helicopter lineman'sladder of claim 1 which is formed of electrically nonconductivematerial.
 7. The helicopter lineman's ladder of claim 1 wherein saidfirst elongate ladder section is at least eleven feet in length.
 8. Thehelicopter lineman's ladder of claim 7 wherein said second elongateladder section is shorter in length than said first elongate laddersection.
 9. The helicopter lineman's ladder of claim 8 wherein saidfirst and second ladder sections are unitary.
 10. The helicopterlineman's ladder of claim 9 wherein said second ladder section extendsangularly from said first ladder section at an angle at least equal toninety degrees.
 11. The helicopter lineman's ladder of claim 10 whereinat least one weight is secured to said conductor engaging base.
 12. Thehelicopter lineman's ladder of claim 11 wherein an elongate flexibletether is connected to said powerline conductor engaging base and aweight is connected to said tether in spaced relation to said powerlineconductor engaging base.
 13. The helicopter lineman's ladder of claim 12which is formed of electrically nonconductive material.
 14. Thehelicopter lineman's ladder of claim 1 wherein said powerline conductorengaging base is formed by an elongate, electrically nonconductive barextending laterally on both sides of said second elongate laddersection.
 15. The helicopter lineman's ladder of claim 14 wherein anelongate flexible tether is connected to said powerline conductorengaging base and a weight is connected to said tether in spacedrelation to said powerline conductor engaging base.
 16. The helicopterlineman's ladder of claim 1 wherein said powerline conductor engagingbase is formed by an electrically nonconductive platform, said platformbeing weighted by at least one weight attached thereto.
 17. Thehelicopter lineman's ladder of claim 4 wherein said angle is definedbetween the underside of said first and second ladder sections.
 18. Thehelicopter lineman's ladder of claim 10 wherein said angle is definedbetween the underside of said first and second ladder sections.